A. Technical Field
The present invention relates to a curable resin composition which is suitably used for various purposes of use, for example, paints, surface treating agents (such as primers and anchoring agents), adhesives, pressure-sensitive adhesives, printing inks, and more particularly, to a curable resin composition which can form a coating film having excellent adhesion to various substrates.
Also, the present invention relates to a laminate film useful as, for example, films for packaging, and to a curable adhesive composition used for an adhesive layer of the laminate film. More specifically, it relates to a laminate film in which a film of thermoplastic resins, for example, polyolefin (such as polypropylene and polyethylene), polyamide, polyester, vinylidene chloride polymer, ethylene vinyl alcohol copolymer, cellophane, is laminated, or a laminate film in which a film of a thermoplastic resin, for example, polyolefin (such as polypropylene and polyethylene), polyamide, polyester, vinyl chloride, cellophane, which can impart strength at relatively low cost, is used as a substrate, and a layer of, for example, vinylidene chloride polymer, ethylene vinyl alcohol copolymer, which imparts a barrier property against moisture or oxygen, is laminated thereon, and to a curable adhesive composition which is used for an adhesive layer of those laminate films.
B. Background Art
Two-liquid type curable resin compositions comprising an oxazoline group-containing polymer and a carboxyl group-containing polymer have been so far investigated Japanese Allowable Patent Publication (Kokoku) No. Showa 63-48884, hereinafter referred to as "JP-B"). Further, methods of beforehand neutralizing carboxyl groups in a carboxyl group-containing polymer with a basic component are also investigated in order to increase stability of a one-liquid type curable resin composition comprising an oxazoline group-containing polymer and a carboxyl group-containing polymer (Japanese Patent Application Publication (Kokai) No. Heisei 7-118548, herein after referred to as "JP-A"). Such curable resin compositions comprising an oxazoline group-containing polymer and a carboxyl group-containing polymer can form a coating film, having excellent performances such as water resistance and chemical resistance, by crosslinking reactions.
However, the above-mentioned conventional curable resin composition comprising an oxazoline group-containing polymer and a carboxyl group-containing polymer are still not sufficient in adhesion to various substrates. For example, JP-A-7-118548 exemplifies dimethylaminoethyl (meth)acrylate as a copolymerizable composition in the copolymer of the oxazoline group-containing polymer and carboxyl group-containing polymer, but adhesion is insufficient with such tertiary amino group- or amido group-containing unsaturated monomers. Further, JP-B-63-48884 exemplifies amino group-containing unsaturated monomers as a co-reactive unsaturated monomers. However, high temperature treatment at 200.degree. C. or more is necessary for the reaction between an amino group and an oxazoline group in order to increase performances of the coating film, such as water resistance and chemical resistance. Therefore, the purposes of use are limited.
On the other hand, primary and secondary amino group-containing polymers represented by polyethyleneimine or the like have good adhesion to various substrates due to the primary and secondary amino groups, and therefore, those polymers are used in wide fields as a primer or the like. Furthermore, where the primary and secondary amino group-containing polymers and primary amino group-containing compounds represented by polyamide amine or the like are used as a paint and an adhesive, it is also investigated to use them as a curable resin composition by mixing a crosslinking agent such as an epoxy compound, in order to increase performances of the coating film, such as water resistance and chemical resistance.
However, the primary and secondary amino group-containing polymers have excellent adhesion to various substrates, but are insufficient in performances of coating film, such as water resistance and chemical resistance. If the crosslinking agent such as the epoxy compound is used in order to avoid this, it suffers problems, on working, of safety such as skin irritation due to the epoxy resin.
On the other hand, in the field of laminate films as a use of the above-mentioned conventional curable adhesive composition, there are the following problems:
That is to say, a laminate film in which a film of thermoplastic resins, for example, polyolefin (such as polypropylene and polyethylene), polyamide, polyester, vinylidene chloride polymer, ethylene vinyl alcohol copolymer, cellophane, is laminated, or a laminate film in which a film of a thermoplastic resin, for example, polyolefin (such as polypropylene and polyethylene), polyamide, polyester, vinyl chloride, cellophane, or the like, which can impart strength at relatively low cost, is used as a substrate, and a layer of, for example, vinylidene chloride polymer, ethylene vinyl alcohol polymer, which imparts a barrier property against moisture or oxygen, is laminated thereon, exhibits functions such as moisture-proof property, and gas barrier property, and are therefore widely used as, for example, packaging films for foods.
In those laminate films, in order to improve interlayer adhesive property and water resistance, it has been practiced at the initial stage to improve surface adhesive property by applying corona discharge treatment, flame treatment, or chemical treatment with alkalis or acids to the surface of the thermoplastic resin film. However, in recent years, in order to meet further demanded performance, it is investigated to provide a layer of an adhesive composition as an adhesive for laminating films on each other in a laminate film, or provide an adhesive composition layer as a primer where a resin layer of vinylidene chloride polymer is coated on a thermoplastic resin film. For example, U.S. Pat. No. 3,023,126 proposes to use a polyurethane primer, and U.S. Pat. No. 4,214,039 proposes to use an aqueous curable primer of acid-neutralized amino group-containing polymer and epoxy resin.
Further, it is already stated about an application of the oxazoline group-containing compound or the primary and secondary amino group-containing polymers.
However, such adhesive compositions, as conventionally proposed, had problems in that: the composition is difficult to handle due to its sensitivity to moisture; the pot life is short and therefore causes problems on workability; and the discoloration occurs during hot water immersion. That is to say, the polyurethane composition, as proposed in U.S. Pat. No. 3,023,126, is sensitive to moisture and therefore difficult to handle. Further, the composition, as proposed in U.S. Pat. No. 4,214,039, is a composition which is an aqueous system comprising acid-neutralized amino group-containing polymer and epoxy resin, and imparts curable adhesive property, so that the pot life after mixing is short, and further, the discoloration occurs during hot water immersion, and thus there is room for further improvement.
Further, even if the curable composition comprising an oxazoline group-containing polymer and a carboxyl group-containing polymer, as disclosed in JP-B-63-48884, is applied to a laminate film, it is insufficient in respect to the adhesion. Furthermore, where the curable composition comprising primary and secondary amino group-containing polymers, as represented by polyethyleneimine, and an epoxy resin is applied to a laminate film, a pot life is produced, and the workability is poor.